The present invention relates to a wireless communication device and a marginal transmission power determining method.
A card type wireless communication device has recently become known. Such a card type wireless communication device is mounted in host equipment such as a note-book size personal computer or the like, and used for wireless communication of the host equipment.
The card type wireless communication device as described above has no power source and operates by using power supplied from the host computer. The host equipment supplies power with a standardized voltage value (for example, 3.3V±0.3V in PC Card Standard). Current input from the host equipment to the wireless communication device (consumption current of the wireless communication device) becomes larger as the power (output) of the wireless communication device becomes larger. However, there are some host equipment that cannot keep the standardized voltage when the current input to the wireless communication device increases to a predetermined current value or more, which means that the voltage value of power to be supplied to the wireless communication device is reduced.
JP-A-11-98845 describes a technique of moderately increasing the output voltage of a sine-wave converter up to a final target value to thereby prevent inrush current from flowing into the sine-wave converter. The inrush current is defined as a large amount of input current that temporarily flows when the consumption current of a device rapidly increases. The inrush current is temporary, and thus the input current is stabilized after a while from the time when the consumption current increases rapidly. The stabilized input current is called stationary current.
However, the recent wireless communication devices have a tendency to have advanced multiplexing of communications and thus the reception power required to carry out demodulation and decoding is increased, which increases the transmission power. When the transmission power increases, the consumption current is increased as described above, and the inrush current when the transmission power is rapidly increased up to the upper limit thereof may exceed the predetermined current value. At this time, the voltage value of power supplied to the wireless communication device is lowered as described above, so that the operation of the wireless communication device is unstable or reset occurs due to voltage drop. Accordingly, it is impossible to continue the communications.
In view of the foregoing problem, it may be considered to moderately increase the transmission power of the wireless communication device up to the final target value, to thereby prevent inrush current from flowing in the wireless communication device, as in the case of the technique disclosed in JP-A-11-98845.
However, if the transmission power is increased at such a speed that no inrush current flows as described above, it would take a long time until the transmission power increasing processing for greatly increasing the transmission power of the wireless communication device is completed.